In order to understand the basis of human genetic disease and to begin to develop procedures by which human developmental anomalies can be treated, it is necessary to develop appropriate animal models and to perform basic research designed to uncover the molecular mechanisms of normal and abnormal development. Progress toward a molecular-genetic description of the embryonic development of invertebrate organisms such as D. melanogaster and C. elegans has been aided by their short generation times. To elucidate the molecular mechanisms by which vertebrate embryos develop, a similar analysis is required. However, inquiries into the molecular-genetic basis of vertebrate development have been hindered by long generation times, and in the case of mammals, inaccessible embryos (i.e., in utero development). In the investigations proposed here, a molecular-genetic analysis of early vertebrate development will be initiated using the zebrafish as a model system. This organism has many experimental advantages relative to mammalian systems, including small size, fecundity, and the natural in vitro development of optically transparent embryos. In addition, it is possible to produce and analyze gynogenetic and haploid progeny, and to produce stable germ-line transformants. Genetic loci likely to be involved in early embryonic development will be identified with the aid of a transgene marker designed to respond to endogenous enhancer-like controlling elements located near the site of integration. The unique expression patterns exhibited by these integrated "enhancer detectors" will provide important clues as to the function of the marked genes. The potential of these transgenes to result in insertion mutations with interesting phenotypes will also be evaluated. The transgenes themselves provide hybridization and/or genetic markers allowing the rapid recovery of flanking sequences at the identified locus. Marked loci will be further characterized by Southern and Northern analysis, allowing the identification of individual genes likely to play crucial roles in development.